Conventionally, suitably blended mixtures of partially hydrogenated oils obtained by hydrogenating animal and vegetable fats and/or oils (hereinafter, referred to as “hydrogenated oil”), vegetable oils being liquid at ordinary temperature and the like are generally used as the raw material fat and/or oil of a plastic fat for confectionary and bakery products. However, such hydrogenated oils contain trans acid residues formed during the hydrogenation process by isomerization of the unsaturated fatty acids which have the same or higher level of unsaturation as linoleic acid. Trans acids are said to substantially increase the risk of cardiac disease, as they increase the level of LDL (so-called “bad cholesterol”) in the blood in the same manner as saturated fatty acids.
Recently, as a result of increased health awareness, fats and fat compositions essentially free from trans acid residues are being demanded. However, with combinations of fully hydrogenated oils (hereinafter, referred to as “extremely hydrogenated oils”) of animal and vegetable fats and/or oils and vegetable oils being liquid at ordinary temperature, there has been the problems that the mouth feel deteriorate as the blended amount of extremely hydrogenated oil increases, while plasticity is lost if the blended amount of extremely hydrogenated oil is decreased.
To solve this problem, attempts have been made to convert the physical properties of the fats by subjecting an extremely hydrogenated oil and a liquid oil to a transesterification process. For example, a fat composition for producing margarine or shortening has been proposed which is a corandomized fat having a melting point (slipping point) of 20 to 50° C. and which is essentially free from trans acids in the bound fatty acid composition, obtained by transesterification of a palm-oil-based fat and a fat containing a saturated fatty acid having 22 carbon atoms as a constituent fatty acid and/or lower alkyl esters of a saturated fatty acid having 22 carbon atoms, and further, if necessary, oils containing an unsaturated fatty acid having 18 carbon atoms as a main constituent fatty acid (see Patent Document 1).
On the other hand, fats which do not rely on a transesterification process have been proposed, such as a fat composition, essentially free from trans fatty acids, comprising 0.5 to 10% by weight of an extremely hydrogenated fish oil, and 3 to 40% by weight of extremely hydrogenated palm kernel oil and/or extremely hydrogenated coconut oil in its oil phase (see Patent Document 2); a plastic fat composition comprising 10 to 40% by weight of a lauric fat with a melting point of 30° C. or higher in the fat component, wherein in the fatty acid constituting that component the saturated fatty acid content is 35% or less and the trans acid content is 5% or less (see Patent Document 3); and a plastic fat composition comprising in the oil phase 40 to 84.5% by weight of a oil which is liquid at 25° C., 0.5 to 10% by weight of an extremely hydrogenated oil having a melting point of 55° C. or higher, and 15 to 50% by weight of a triacylglycerol represented by SLOSL (SL being saturated fatty acids having 16 to 22 carbon atoms, and O being oleic acid) (see Patent Document 4).
However, even fat compositions obtained by the above-described methods suffer from the drawback of lost smoothness as a result of the fat crystals becoming coarser due to a change in the crystal state of the fat during storage.    Patent Document 1: Japanese Laid-Open Patent Publication No. Sho 62-81497    Patent Document 2: Japanese Laid-Open Patent Publication No. Hei 9-143490    Patent Document 3: Japanese Laid-Open Patent Publication No. 2002-161294    Patent Document 4: Japanese Laid-Open Patent Publication No. 2004-204067